Barannik, E. A., O. S. Kostyreva, and A. I. Marusenko. “Nonlinear Effects Influence to Ultrasound Beams Spatial Distribution and Focusing”. Biophysical Bulletin, Vol. 2, no. 23, June 2009, pp. 106-13, https://periodicals.karazin.ua/biophysvisnyk/article/view/17002.